December 13, 2005
09:00 AM (EST)

News Release Number: STScI-2005-36

Astronomers Use Hubble to 'Weigh' Dog Star's Companion

December 13, 2005: For astronomers, it's always been a source of frustration that the
nearest white-dwarf star is buried in the glow of the brightest star in
the nighttime sky. This burned-out stellar remnant is a faint companion
of the brilliant blue-white Dog Star, Sirius, located in the winter
constellation Canis Major. Now, an international team of astronomers has
used the keen eye of NASA's Hubble Space Telescope to isolate the light
from the white dwarf, called Sirius B. The new results allow them to
measure precisely the white dwarf's mass based on how its intense
gravitational field alters the wavelengths of light emitted by the star.

This Hubble Space Telescope image shows Sirius, the brightest star in
our nighttime sky, along with its faint, tiny stellar companion, Sirius B.
Astronomers overexposed the image of Sirius [at center] so that the dim
Sirius B [tiny dot at lower left] could be seen. The cross-shaped
diffraction spikes and concentric rings around Sirius, and the small
ring around Sirius B, are artifacts produced within the telescope's
imaging system. Sirius B is a white dwarf that orbits around Sirius
every 50 years. Sirius, only 8.6 light-years from Earth, is the fifth
closest star system known.